During reeling of a thread through a thread guide moving to-and-fro along a bobbin, tension and the speed of the thread fluctuates for various reasons. At the points of reversal of the traversing, the angle of inclination of the helical groove in the rotary cam drum changes to zero and then increases in the return direction to a maximum value. Due to the change in the angle of the inclination, the thread speed continually changes during the to-and-fro movement of the thread. However, even though the thread speed changes, the peripheral speed of the bobbin on which the thread is reeled remains constant. Consequently, the tension of the thread varies considerably as it is reeled onto the bobbin.
The effect of the so-called thread triangle is to bring about a change in the speed of the thread during the to-and-fro movement of the thread. The thread triangle is defined by the two points of reversal of the thread guide member of the thread guide assembly and the upper fixed point in the thread guidance which is situated in general at a spacing above the middle of the traversing travel of the thread guide member. This spacing or length of the helical groove between the reversal points should be as large as possible for the reduction of the speed differences along the thread lengths travelling through the thread triangle. In general, the spacing amounts to two to four times the traverse which is the shortest distance between the two reversal points. When the thread guide member moves from the middle of the traverse to one extreme position of the same, the distance between the thread guide and the fixed point increases. Thus, because of this variation, there is an increase in the speed of the thread as the bobbin revolves with a constant peripheral speed. The same applies in the contrary sense with opposite movement of the thread from the end point of the traverse to the middle of the traverse.
The thread is supplied from a processing machine to the reeling assembly at a constant speed. The thread tension continuously changes because of the above-described unavoidable speed variations during the reeling or winding procedure. The effect of such tension changes can also be observed in the product manufactured with the thread. Because of the high cost and large overall size requirements, the so-called thread triangle cannot be made very long. As a result, the so-called triangular tension becomes intolerable during very high thread speeds. As a thread speed increases, additional tension is introduced to the thread due to air friction.
Repeated attempts have been made to overcome these difficulties. In one well known apparatus, the thread is lead around two godets which are driven at a speed higher than the speed of the friction roller. With this known apparatus, the drives must be coordinated in total synchronization with respect to each other. There is a considerable consumption of power in this known apparatus. With lesser overall height of the thread triangle, there exists the danger that the length available for the stretching of the thread is sufficient thereby count fluctuations may arise.
In another known apparatus, a grooved roller is connected downstream of the thread guide of the rotary cam drum. The thread is led directly to the reeling bobbin from the grooved roller. The groove is deeper at the points of reversing than between the latter. The purpose of such grooved roller is to reduce the high triangular tension resulting from guiding the thread in the thread triangle. There are several drawbacks with such grooved rollers. The preparation with which the thread is invested deposits in the grooves, so that the guidance through the groove is uncontrollably changed. Relatively early wear occurs at the groove bottom surface. The direct passing of the thread from the grooved roller to the thread package may impair the product of the winding. Furthermore, the rotational speed of the grooved roller has to be in a certain relationship with respect to the rotational speed of the rotary cam drum or the traversing device. Operation of this combination is tied to a precise relationship of the relative speeds.